Re: /var/log/messages doesn't have crash info when kernel gets panic/oops/crash

Dharmosoth Seetharam
2009-06-13T15:07:37Z

> -----Original Message-----
> From: ebiederm@xmission.com
> Sent: Sat, 13 Jun 2009 07:08:50 -0700
> To: dseetharam@inbox.com
> Subject: Re: /var/log/messages doesn't have crash info when kernel gets
> panic/oops/crash
>
> Dharmosoth Seetharam <dseetharam@inbox.com> writes:
>
>>>>> Basic questions.
>>>>> 1) Do you have panic on oops set?
>>>>> I think that setting more than anything else will be the
>>>>> difference in what shows up in /var/log/messages.
>>>>
>>>> Yes, in my case panic_on_oops was set with 1
>>>
>>> That is the reason thing don't show up in /var/log/messages
>>> because you panic before syslog has a chance to write the messages.
>>
>> Thanks.
>> So, if panic_on_oops set with 0(default), we will get all the
>> needed info like stack traces, bug info etc. in /var/log/messages then
>> reboots.
>>
>> Or do we need to apply any specific patches to get info in
>> /var/log/messages?
>>
>>>
>>>>> 2) Have you tried a dry run and confirmed you can get a crash dump?
>>>>
>>>> No, I haven't tried this.
>>>
>>> It sounds like you have not been getting the coredumps when problems
>>> happen. Running a simple test run to Alt-sysrq-c to confirm
>>> that things are basically setup ok is a good idea.
>>>
>> Sorry, I misunderstood your question.
>> I have gave dry run and confirmed that the dumps are getting saved in
>> particular dir and able to analyze.
>>
>> I did in both the ways like
>> 1 - echo c > /proc/sysrq-trigger
>> 2 -Alt -sysrq -c
>
> Then unless you are having problems capturing core dumps in real
> failure situations it sounds like all is well with the world.
>
> A kernel oops is normally not fatal and the kernel tries to limp along
> allowing for better diagnostics etc. This allows klogd to read the
> kernels message buffer and pass the kernel messages to syslog which
> writes the messages to /var/log/messages.
>
> After a kernel panic nothing is allowed to happen which prevents
> user space from writing to /var/log/messages in the usual way.
>
> If you want data in /var/log/messages it appears you have two choices.
> 1) Post process a core dump as Neil suggested and feed the kernel log
> buffer to syslog.
> 2) disable panic on oops. The system will continue to limp along
> allowing
> user space to write to /var/log/messages.
>
> Eric

Thanks Eric.

I will try all the ways as you suggested and let you know the outcome.

regards,
Seetharam

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